1. Field of the Invention
The present invention relates to a wagon for agricultural use having an all-wheel steering mechanism. Specifically, the invention relates to an all-wheel steering mechanism for a four-wheeled wagon for use in the nursery industry.
2. Prior Art
In the nursery industry, it is common practice to use various types and sizes of wagons for the day to day transportation of plants and materials. Often the layout of the nursery is such that there is little room for these wagons to maneuver safely, without destroying nursery stock.
In general, wagons are designed with two-wheel steering. These wagons have a steerable set of front wheels, and a set of back wheels which are fixed in the forward direction. The steerable front wheels of the wagon are attached to a wagon tongue, which is attached to a tow vehicle. Turning the tow vehicle pivots the tongue, turning the front wheels of the wagon. The inherent problem with this design is that when turning, the back wheels follow a shorter path than the front wheels, which requires the operator to make a wide turn to prevent destruction of the nursery stock while turning. This problem becomes more noticeable among longer length wagons, where a great deal of room is required at the end of the row to allow the wagon to turn safely.
One solution to this problem is to steer both the front and back wheels of the wagon. This is preferably accomplished by a mechanism that translates the steering alignment of the front wheels to the back wheels. Generally, as the front wheels are turned in a certain direction, the back wheels are designed to turn in the corresponding opposite direction. The result is that the back wheels follow in the same path as the front wheels, effectively allowing the wagon to be turned in a much shorter distance.
A known mechanism used to translate the steering alignment to the rear wheels uses diagonal tie bars attached to the front and rear axles. One member is attached to the left side of the front axle, and the right side of the rear axle; whereas, the other member is attached to the right side of the front axle and the left side of the rear axle. As a result, as the front axle is steered in one direction by the tongue, the rear axle is steered in the opposite direction by the diagonal members. While this method accomplishes the desired four wheel steering action, it also has drawbacks. For example, as the diagonal members must be positioned at the level of the wheel axles, it seriously limits the ground clearance of the wagon. This exposes the steering mechanism to potential damage from obstructions. This method also has limitations as to the precision of the steering alignment, as a small imprecision in the placement of the diagonal members will result in a substantial difference between front and rear steering.
Another drawback associated with all-wheel steered wagons is their tendency towards tipping. This is especially prevalent when turning the wagon sharply on uneven terrain or with a top-heavy load. It is therefore desirable to provide means to enhance the stability of the wagon, especially over uneven terrain.
According to this invention, there is provided an all wheel steerable wagon, that has a frame with attached front and rear axles. The axles have wheels pivotally attached to their ends. A front steering linkage is operably connected to the front wheels for tracking their steering alignment and a rear steering linkage is operably connected to the rear wheels. A transmission linkage is attached to the underside of the frame, operably inter-connecting the front and rear steering linkages, for translating the steering alignment of the front wheels to the rear steering linkage to impart a complementary steering alignment to the rear wheels, where the imparted steering alignment is a direct function of the steering alignment of the front wheels.
The transmission linkage consists of a shaft. The operable interconnection between the front steering linkage and the shaft rotates the shaft in response to movement of the front steering linkage. The operable interconnection between the shaft and the rear steering linkage moves the rear steering linkage in response to rotation of the shaft. Each steering linkage consists of a rod member and each operable interconnection consists of a crank fixedly attached to the shaft and pivotally attached to each rod member. The shaft is centrally mounted along the longitudinal axis of the wagon and each rod is aligned transversely to the shaft.
The front axle is connected to the frame of the wagon by a horizontal pin at substantially the midpoint of the axle, allowing the axle to pivot angularly about the pin in response to uneven terrain. The frame has stops integrally formed into it that are operable to limit the angular pivoting of the axle to thirty degrees by contact of the axle with the stops.
Further features of the invention will be described or will become apparent in the course of the following detailed description.